Protection of electrical apparatus from overloads



Aug.- 31 1926. 1,598,406

. H. TINSLEY ET AL PROTECTION OF ELECTRICAL APPARATUS FROM OVERLOADS Filed Feb.- 12, 1926 Patented Aug. 31, 1926.

HORACE TINSLEY, or LEEDS, AND JOHN HENRY COX, F OUTWOOD, ENGLAND, AS

SIGNORS TO DIAMOND GOAL-CUTTER COMPANY LIMITED, OF STENNARD WORKS,

ENGLAND.

PROTECTION OF ELECTRICAL APPARATUS FROM OVERLOADS.

Application filed February 12, 1926, Serial No.

This invention relates'to overload trip or cut-out mechanismof the solenoid and plunger type for the protection from over loads of electrical apparatus and connections thereto, more particularly apparatus which is used to control motor driven machinery.

This mechanism however is as usually constructed set to allow for the sudden rush of current which occurs on closing a starting 1 switch with a stationary motor and in such cases it is not possible to obtain a closer setting for the trip or cut-out mechanism than 150 per cent of full load, whereas in many cases cables and other parts of the electrical apparatus are undesirably heated by currents which are not quite sutiicient to operate the trip mechanism. The chief ob ject of the present invention is to allow in an improved manner for the primary rush of current in the apparatus and consequently in the aforesaid solenoid and at the same time permit the trip or cut-out mechanism to be set to any desired approximation to full load.

a In the present apparatus, therefore, means are provided whereby, at starting, the trip or cut-out mechanism is not ermitted to act upon the usual initial rus of current and according to this invention the support or platform carrying one element of the overload cut-out solenoid and plunger mechanism is moved from the starting to the normal running osition through a resilient connection an under the influence of a delay action device, such as a dashpot, which determines the time taken for the said movement. In the starting position the plunger is sufficiently out of the solenoid I to require an excess of current greater than the usual sudden starting current to produce a field in the solenoid'sutficiently strong to move the plunger while, in the normal running position, the plunger is in a more favourable position for action by the sole noid field and can be operated by a current exceeding the normal full load by any predetermined smaller amount.

In order that the said invention may be clearly understood and readil carried into effect, the same will now be escribed more fully with reference to the accompanying drawing, which illustrates in section a typical construction of apparatus in accordance with this invention, the left and right hand 87,842, and in Great Britain September 17, 192

sides of the figure showing respectively the starting and running positions.

A is the solenoid overload coil within which moves the plunger B, supported on the platform or crossbar C which is moved in the downward direction by the cam F on the switch operating spindle through lever G and push rod 9 and is moved in the upward direction by springs H through the medium ofrods 11 the speed of such movements being controlled by the dashpots J. The time lag of the dashpots in variable through the pressure exerted by the s rings H, which in turn is varied by position of the screwed rod 71 relative to the crossbar C. The platform shown at the left hand part of the drawing in the position it occupies when the switch is oti and when the switch is initially closed, while the right hand part of the drawing shews the'platform in the position it assumes after a short space of time after the switch is closed, such time being governed by the dashpots and being sufficient to allow the motor to get up to its full load speed.

The drawing illustrates an arrangement with three solenoids, plungers and their individual dashpots together with two (lashpots for the time lag on the sensitive vary ing device, but of course the number re quired may be varied or a single self-contai'ned element may be employed.

The platform C moves parallel with the solenoid axis or and according to its position it determines the length of the air gap inside the solenoid A between the plunger l3 and the top pole piece (2 lVhen the platform C is in its lower position as shown at the left hand part of the drawing, the air gap is at its maximum and the pull on the plunger B due to the initial rush of current in the solenoid is not sufficient to raise the plunger from the platform and operate the trip or cutout mechanism while in the normal running position shewn at the right hand part of the drawing, the air gap between the plunger and pole piece is smaller and a smaller current will effect the operation.

The solenoids are mounted within the lower chamber of the casing E and are socurd between the partition e and the bottom 6 of the casing.

The solenoid operated plunger B is guided axes,

guiding nipple c titted to the inner wall no connected by a rod i E a ow end to a hall 72 held in the which slides upon the \lOWDWP-ldcalibration tuhe (Z fixed to the which tuhc the plunger 13 n: a small clearance. The lower dashpot D titted to the plat torm rr is stahie to give any individual setting: ired and may he adjusted l) v a screw action and he" in adjmetedv position l v the siting; engaging in the set of grooves (I:

i when the har C is in s r "t in the left hand l illYlil i the plunger B is lowerantiallv he vond the position ot t i eliiciencv of t solenoid A so ralil c higher than norafse it troai the through the action ot' the so e- The platform or maxi: that a current con:- and would he necew platform C noid upon the core B.

oar C 3, therefore. arranged to take up th s position when the switch is oil and on stai cmotor, while when the switch ing: the

moved over into normal atingr arm nine pt tion the spring; connection to oar raises tire latter into the position sho n in the r. 1 hand part ot the dra in ra hut the movement is etl'ected through the delay action of the dashpot and time is conseuent v given or the displacement into the normal running position so that the sudden starting rush of current is ineilective in operzn the trip mechanism, wnile atter the har is raised the plunger 1) is in its more ei'licient position. and a small excess 0t current over the normal will li'tt the plunger and operate the trip mechanism.

What we claim and desire to secure by Letters Patent ot the United States is 1. In overload protection mechanism for electrical apparatus, a lined casing. a solenoid and plunger cut-out device carried by the said casing, a support for one element ot the solenoid and plunger device displacealne axially ot the solenoid, means tor moving the support from the starting to the normal running position of the mechanism and a dela v action device which determines the time taken for said movement, which device is mounted between the said support and casing.

2. In overload protection mechanism for elec'rical apparatus, a fixed casing, a solesaid support from the noid and plunger cut-out device, a displaceahle support for one element of the solenoid and plunger device, means l'or moving the starting; to the normal. running position of the mechanism and a dashpot havingtwo era-operating; memhers 01? which one is carried by the said movable support and the other h the casing.

3. In overload proteetimi mechanism as in claim 2, means by which the dashpot member carried hy the support adjur' tahle relatively t0 the support.

in overload protection mechanism as in claim 2, means by which the dashpot member carried by the support is screwed adjusiahlv into the said support and is provided with means retaining it in adiustahle position.

5, In ove load protection mechanism for electrical apparatus. a plurality o'i't solenoid and plunger cut-out devices. a displaccahle support carrving one element of each of the solenoid and plunger devices. means for moving the said support from the starting to the normal running; position of the mechanism and a delay action device which determines the time taken for the said latter i'uovemeiit the action of the said lilcllllt'd.

(3. In overload protection mechanism for electrical apparatus, a casing, a partition dividing); the said casinginto two chambers, a ph'u'ality oi: solenoids secured in one oi: the said chambers plungcrs adapted to slide axially within the said solenoids, dash ot devices. one for each plunger and each having two co-operatin; niemhers one of which is fixed in the outer wall of the said casing and has the said plunger sliding within it. a movahle platform to which the other dashpot members are adjusta 'll v secured, connections between the planners and their respective dashpot memhers carried by the said plattorm, springs tending to move the ilattorm and attached members from a starting position to a normal runnin; position for the apparatus a cam mounted with in the second chamher ot the casing and a push rod connected to the dashpot platl'orm and projecting into the said chamher. which push rod is adapted to he actuated hy the said cam to displace the plattorm and as sociated members from one position to the other under the control of the springs and dashpots. 

